Liguy, with respect, the Home Depot cords are horrid. I happen to have made some for myself years ago when I was first experimenting with comparisons of power cords. I thought I was genius to get "top quality" sound on the cheap. But when I compared the Home Depot Home made to even approx. $100 power cords by the likes of Audioquest or Wireworld the H.D. cord sucked - that is sucked the life right out of the music. I couldn't stand to use them and got rid of them quickly. It was a waste of time and money, except for the fact that it reinforced the point that the cable manufacturers know what they're doing and the typical DIY guy does not.
Since I cannot prove otherwise, it may be that on your rig alone, given you have "hyper-power supplies" you designed, there may not be a difference in sound between power cords. OTOH, you suggest that some manufacturers of high end audio gear are getting it right. What if those amps also exhibited sonic differences with various power cords? Then where would you go in your argument?
I will say this, having worked with some of the finest audio equipment available, some with dedicated, optimized power supplies such as with the VAC Signature Preamplifier MkII (reviewed for Dagogo.com), not a one, not a single component I have ever come across has been impervious to power cord idiosyncrasies. I simply do not accept that when the dielectric, total gauge, conductor material etc. is changed on a cable the net result is nil sonically. I have used too many cables and too many components to concede that.
Liguy, you're a nice asset to this discussion and our little group here. I wish you could make a visit and we could test out some of our theories. I would find it fascinating to hear your rig and the power supplies you have made.
Dave (Corazon), the answer to your question is that manufacturers do not want to paint themselves into a corner with cables. If they don't believe in aftermarket power cords they're not going to promote them. If they do find them useful, they're not going to get in bed with one cord manufacturer or else they cut their fan base. Further, they may know that a particular cord renders a specific sound with their gear and it may not appeal to all listeners with all systems. Better to let the masses figure it out on their own.